The present invention relates to a broadband receiver, and more particularly to a broadband receiver comprising a frequency counter for measuring the frequency of reception signals.
A broadband receiver is known wherein a signal having a strong reception intensity is automatically identified from the radio waves being transmitted through a radio space, the frequency of that signal is measured by a frequency counter, and the oscillating frequency of a local oscillator is adjusted in such a manner that the reception frequency coincides with the measured frequency. A broadband receiver of this type is used, for instance, when intercepting third-party radio communications, or the like.
U.S. Pat. Nos. 5,471,402 and 5,710,710, for example, are known as patent references relating to a frequency counter.
However, in a conventional broadband receiver, there have been problems in that the local oscillation signal output by the local oscillator is taken in by the frequency counter and may cause malfunction of the frequency counter or degrade the sensitivity of the counter.
Furthermore, if a radio wave is emitted by a pager, or the like, which does not need to be received but which has a strong reception intensity, and if this wave is within the reception waveband of the frequency counter, then in a conventional broadband receiver, this unwanted wave will be always detected when a search is made for a signal having a strong reception intensity. Therefore, hence problems have arisen in that the reception frequency is made to coincide with the frequency of the unwanted radio wave.
Moreover, in a conventional broadband receiver, after detecting a signal having a strong reception intensity and receiving that signal, when the receiver searches for a new signal having a strong reception intensity, it may detect a signal that has already been detected in the past, again, and hence a problem arises in that the search for new signals becomes difficult.
Furthermore, when measuring the frequency of the reception signal by means of a frequency counter, it is possible to increase measurement accuracy by lengthening the cycle of the frequency counter, but a large amount of time is required in order to separate the noise from the signal. On the other hand, if the cycle of the frequency counter is shortened, the time required to separate the noise and the signal can be reduced, but the accuracy of the frequency measurement declines. Furthermore, if a method is adopted wherein a frequency counter having a short cycle is activated a plurality of times, the frequency being calculated by adding up the respective measurement values, then it is not possible to obtain sufficient accuracy in the frequency measurement, due to the accumulation of the measurement errors in each measurement operation.
It would be a significant advance in the art to provide a broadband receiver whereby (i) interference caused by a local oscillator with respect to a frequency counter can be reduced, (ii) previously determined unwanted radio waves are not received, (iii) prior received signals are not received again when searching for a new signal, and (iv) highly accurate frequency measurement can be achieved in a short period of time.